1. Field of the Invention
The invention relates to a hole saw. More particularly, the invention relates to a hole saw having a tapered pilot drill which allows for rapid and easy removal of a cut plug from the hole saw.
2. State of the Art
Hole saws are well known in the art and a typical hole saw is shown in prior art FIG. 1. The prior art hole saw 10, generally includes a mandrel 12 having a central cylindrical pilot drill bit 14, and an annular cutting saw blade 16. The saw blade 16 is substantially cylindrical with cutting teeth 16a at its distal end and a mounting flange 16b at its proximal end, defining a cylindrical space 16c therebetween. The mounting flange 16b is coupled to the mandrel 12 so that the saw blade 16 is substantially coaxial with the pilot 14. Mandrel 12 is provided with a proximal shank 18 which is typically sized to fit a conventional hand operated power drill (not shown).
The hole saw 10 is used by attaching the shank 18 to a power drill and aligning the point of the pilot drill 14 with the center of a circle to be cut out of a board or the like (not shown). The pilot helps to center the hole saw as the hole is being cut. As the pilot 14 advances through the board, the annular saw blade 16 eventually engages the board and begins to cut a circular hole around the pilot. When the blade 16 passes through the board, an annular plug is removed from the board. The plug resides on the pilot 14 and within the cylindrical portion of the saw 16 and must be removed from the hole saw 10. Depending on the material which is cut, removal of the plug from the saw can be quite difficult and may require removal of the blade 16 from the mandrel 12.
There have been many attempts to design a better hole saw in which removal of the cut plug is facilitated. U.S. Pat. No. 2,473,077 to Starbuck, Jr. discloses a trepanning tool which is similar to the hole saw 10 shown and described above. The trepanning tool has helical slots in the cylindrical portion of the saw. A cut plug can be removed from the saw by inserting a suitable tool into one or more of the slots to push the plug out of the saw. U.S. Pat. No. 3,648,508 to Hougen provides a knock-out hole in the base of the saw which can be used with a suitable tool in a similar manner. Both of these hole saws require the use of an additional "suitable tool" in order to remove the plug from the saw.
U.S. Pat. No. 3,825,362 to Hougen discloses a hole saw having a spring biased cylindrical pilot having a pointed tip (see, e.g. FIGS. 1-4) or a recessed tip (see, e.g. FIGS. 11-15). In theory, the pilot will only penetrate the board up to the base of the tip or the point of the step in the pilot and the biasing spring will push the pilot carrying the plug out of the saw. While possibly effective, this device is unusually complex and relatively expensive to manufacture.